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VII. — Rupture Stresses in Beams and Crane Hooks. By Angus R. Fulton, 

 B.Sc, A.M.Inst.C.B., Engineering Department, University College, Dundee. 

 Communicated by Professor A. H. Gibson, D.Sc, A.M.Inst.C.E. 



(MS. received November 4, 1913. Read February 16, 1914. Issued separately April 15, 1914.) 



I. Bending Moment as in a Beam. 



In connection with a research into the failure of timber under stress, carried out 

 by the author, and on which a paper was read before the Royal Society of Edinburgh 

 and published in their Transactions* many of the tests were made by cross-breaking. 



The probable development of the stress diagram of a beam of rectangular section, 

 supported at two ends and loaded in the middle where the tensile and compressive 

 strengths of the material are of different values, was illustrated in fig. 38 of that 

 paper. It was there laid down that when the fracture point was ultimately reached 

 either (a) the tension and compression stress areas both assume the rectangular 

 form and are equal to each other, the stress ordinates respectively being equal to 

 the ultimate breaking stresses of the material in direct tension and compression ; or 

 (b) the cohesion between adjacent fibres measured from the neutral axis outwards is 

 not sufficient to withstand the shear induced by the resisting moment of the beam, 

 a shear which is at a maximum along the neutral axis of the beam. 



These assumptions made for the case of beams of rectangular sections might be 

 said to have found verification in the experiments on such beams of various timbers 

 supported at two ends and loaded in the middle, the results of which were tabulated 

 in that paper. 



Experiments on Cast-iron Beams. 



Since then the author has carried out a number of similar tests on rectangular 

 beams made of cast iron, a material which differs from timber in that it apparently 

 possesses no plastic stage such as characterises the latter. 



The specimens used for the purpose of obtaining direct tensile and compressive 

 stresses were cast from the same melting as the beams and so were directly comparable. 



The average values obtained for these direct stresses were : — 



Cast Iron. 

 Tension stress, T= 9*5 tons per sq. in. 



Compression stress, C = 45 '5 ,, ,, ,, 



The dimensions of test pieces used in compression were 2-f in. long and 1^ in. 



xf in. 



The formula as derived in the paper referred to, and presumably applicable to all 



* Trans. R.S.E., vol. xlviii., 1912, pp. 417-440. 

 TRANS. ROY. SOC. EDIN., VOL. L. PART I. (NO. 7). 29 



